Organoiridium compound, process for producing the same, and process for producing film

ABSTRACT

An organometallic iridium compound having low melting point, excellent vaporization characteristic and low film formation temperature on a substrate, a process for producing the compound, and a process for preparing iridium-containing films using the organometallic compound are provided. 
 
The organometallic iridium compound represented by the formula (1)  
                 
 
(example of specific compound: (ethylcyclopentadienyl)bis(ethylene)iridium) is obtained by reacting a compound represented by the formula (4)  
                 
 
with a compound represented by the formula (2) or (3)  
                 
An iridium-containing film is prepared using the compound as a precursor. 
 
In the formulae, R 1  represents hydrogen atom or a lower alkyl group; R 2  represents a lower alkyl group; X represents a halogen atom; and M represents an alkali metal.

TECHNICAL FIELD

The present invention relates to an organometallic compound that can bea material for preparing iridium-containing films on substrates, aprocess for producing the compound, and a process for preparingiridium-containing films.

BACKGROUND ART

In integrated circuits in recent years, ferroelectric memories usingresidual polarization of ferroelectrics are eagerly investigated.Specifically, lead zirconate titanate (PZT: Pb(Ti, Zr)O₃), strontiumbismuth tantalate (SBT: SrBi₂Ta₂O₉), and the like are investigated. Aselectrode materials of those ferroelectrics, noble metal thin films ofruthenium, platinum, iridium, and the like, or oxide thin films of thesenoble metals become necessary. In particular, iridium and iridium oxideare considered to be a leading part of electrode materials in thefuture. As the production process of iridium and iridium oxide thinfilms, a sputtering process and a chemical vapor deposition process (CVDprocess) are employed. In particular, the CVD process is considered asthe mainstream in the production process of thin film electrodes in thefuture for the following reason. The CVD process is liable to produceuniform films, and also has excellent step coverage, and therefore, thisprocess can be compatible with higher density formation to the recentcircuits and electronic parts.

As precursors for forming thin films using this CVD process, it isconsidered that among metallic compounds, organometallic compounds thathave low melting point and are easy to handle are suitable. Hitherto,tris(dipivaloylmethanato)iridium, tris(acetylacetonato)iridium,(cyclopentadienyl)(1,5-cyclooctadiene)iridium, and the like have beeninvestigated as an organometallic compound for the purpose of depositingan iridium or iridium oxide thin film. Those iridium compounds have highstability in the atmosphere and are non-toxic, and therefore, haveaptitude as a precursor of CVD. However, those iridium compounds aresolid at ordinary temperatures and involve such a problem thatvaporization of the precursor and transportation to a substrate aredifficult.

In recent years, iridium complexes having a low melting point areeagerly investigated. As a measure of making the iridium complexes havea low melting point, there is a measure to form a compound in which atleast one hydrogen atom on a cyclopentadienyl ring incyclopentadienyl(1,5-cyclooctadiene)iridium is substituted with an alkylgroup.

For example, as cyclopentadienyl derivatives,(1,5-cyclooctadiene)(ethyl-cyclopentadienyl)iridium is disclosed (forexample, JP-A-11-292888). Since this metallic compound is liquid atordinary temperatures, and its melting point is low as compared withthat of (cyclopentadienyl)(1,5-cyclooctadiene)iridium, it is consideredthat this compound is possessed of characteristics necessary as theprecursor applied to the CVD process. However, this compound hasextremely high stability, and the decomposition temperature of thecomplex is high. Accordingly, it is inevitably required to increase thesubstrate temperature at the time of film formation. As a result, thereis encountered such a problem that the step coverage at the time offilm-formation is poor. There is further encountered such a problem thatan iridium oxide film is difficult to be formed. In the meanwhile, as areport of iridium complexes having ethylene and cyclopentadienyl groupas regands, there is a synthesis example of(cyclopentadienyl)bis(ethylene)iridium (for example, see M. Dziallas, A.Hohn and H. Werner, J. Organomet. Chem., 330 (1987) 207-219). However,the compound is solid at room temperature and is not suitable as CVDmaterials.

DISCLOSURE OF THE INVENTION

The present invention has been made in view of the above technicalproblems. That is, the present invention relates to an organometalliccompound that can be a precursor for preparing iridium-containing films,and the objects are to provide the organometallic compound having a lowmelting point, excellent vaporization characteristics and low filmformation temperature on a substrate, a process for producing the same,and a process for preparing iridium-containing films using theorganometallic compound.

The present inventors have made extensive and intensive investigationsto solve the above-described problems. As a result, a novel iridiumcomplex exhibiting a melting point such that it is liquid at roomtemperature and having good vaporization characteristics anddecomposition characteristics has been developed by introducing a loweralkyl group into a cyclopentadienyl ring (hereinafter referred to as “Cpring”) or ethylene of (cyclopentadienyl)bis(ethylene)iridium.

The present invention provides an organometallic iridium compoundrepresented by the following general formula (1):

wherein R₁ represents hydrogen atom or a lower alkyl group; and R₂represents a lower alkyl group.

The present invention further provides a process for producing theorganometallic iridium compound represented by the general formula (1),which comprises reacting a compound represented by the following generalformula (4):

wherein R₂ represents a lower alkyl group, and M represents an alkalimetal, with a compound represented by the following general formula (2)or a compound represented by following general formula (3):

wherein R₁ is the same as defined above, and X represents a halogenatom,

wherein R₁ and X are the same as defined above.

The present invention further provides a process for preparingiridium-containing films, which comprises using, as a precursor, theorganometallic iridium compound represented by the general formula (1).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing GC/MS chart of the iridium compound obtained inExample 1.

FIG. 2 is a view showing decomposition characteristics of the iridiumcompound obtained in Example 1.

FIG. 3 is a view showing decomposition characteristics of(1,5-cyclooctadiene)(ethylcyclopentadienyl)iridium obtained inComparative Example 1.

FIG. 4 is a view showing GC/MS chart of(methylcyclopentadienyl)bis-(ethylene)iridium obtained in Example 2.

FIG. 5 is a schematic view of an equipment of the CVD process used inExample 3.

In the drawings:

-   -   1: Precursor container    -   2: Oil bath    -   3: Reaction chamber    -   4: Substrate    -   5: Oxidation gas    -   6: Counter gas    -   7: Carrier gas    -   8: Mass flow controller    -   9: Mass flow controller    -   10: Mass flow controller    -   11: Vacuum pump    -   12: Exhaust

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in detail below.

Definition of the terms used in the present specification and specificexamples thereof will be described.

The term “lower alkyl group” used herein means a straight-chain,branched or cyclic alkyl having 1-6 carbon atoms. Therefore, examples ofthe lower alkyl group used in R₁ and R₂ include methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl,neopentyl, tert-pentyl, 1-methylbutyl, 2-methylbutyl,1,2-dimethylpropyl, hexyl, isohexyl, 1-methylpentyl, 2-methylpentyl,3-methylpentyl, 1,1-dimethylbutyl, 2,2-dimethylbutyl, 1,3-dimethylbutyl,2,3-dimethylbutyl, 3,3-dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl,1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-1-methylpropyl,1-ethyl-2-methylpropyl, cyclopropyl, cyclobutyl, cyclopentyl,cyclohexyl, cyclopropylmethyl, 1-cyclopropylethyl, 2-cyclopropylethyl,and cyclobutylmethyl.

In the present invention, R₁ represents hydrogen atom or a lower alkylgroup. R₁ is preferably methyl or hydrogen atom, and more preferablyhydrogen atom. On the other hand, in the present invention, R₂represents a lower alkyl group. The lower alkyl group is preferablymethyl, ethyl, propyl or butyl, and more preferably methyl or ethyl. Inthe present invention, X represents a halogen atom. Examples of thehalogen atom include fluorine, chlorine, bromine and iodine. Of those,chlorine or bromine is preferable. In the present invention, Mrepresents an alkali metal. Examples of the alkali metal includelithium, sodium and potassium. Of those, lithium or sodium ispreferable.

The organometallic iridium compound represented by the general formula(1) of the present invention can be obtained by reacting the compoundrepresented by the general formula (4) with the compound represented bythe general formula (2) or the compound represented by the generalformula (3). Reaction conditions in such a reaction are not particularlylimited. For example, the two compounds each may be added to appropriatesolvents, respectively, and the respective solutions may be mixed andreacted at low temperature. Post-treatment is not particularly limited.Generally employed method is that a mixed solution after completion ofthe reaction is concentrated; the desired compound is extracted from theresulting mixture using an organic solvent such as pentane, hexane orether; an appropriate carrier is selected; the extract is subjected tocolumn chromatography using the appropriate solvent as an eluant; andthe extract is subjected to distillation. Thus, the desiredorganometallic iridium compound can be obtained.

An iridium-containing film can be produced using, as the precursor, theorganometallic iridium compound represented by the general formula (1)of the present invention. Specific means for such a production processis not particularly limited. For example, any of CVD process, atomiclayer deposition process (ALD process), and spin coating process may beused.

In the case of producing the iridium-containing film by CVD process, ALDprocess or the like using the organometallic iridium compoundrepresented by the general formula (1) of the present invention, amethod of supplying the precursor to a film-formation chamber is notparticularly limited. For example, a bubbling process may be used, and aliquid injection process may also be used.

In the present invention, in the case of producing theiridium-containing film by CVD process or ALD process, theorganometallic iridium compound may be used as it is, or may bedissolved in an organic solvent and then used as an organometalliciridium compound solution.

Examples of the organic solvent that is used in the case of using as asolution include alcohols (for example, methanol, ethanol orisopropanol), esters (for example, ethyl acetate, butyl acetate orisoamyl acetate), glycol ethers (for example, ethylene glycol monoethylether, ethylene glycol monomethyl ether or ethylene glycol monobutylether), ethers (for example, diethyl ether, glyme, diglyme, triglyme ortetrahydrofuran), ketones (for example, methyl butyl ketone, methylisobutyl ketone, ethyl butyl ketone, dipropyl ketone, diisobutyl ketone,methyl amyl ketone or cyclohexanone), and hydrocarbons (for example,hexane, cyclohexane, ethylcyclohexane, heptane, octane, benzene, tolueneor xylene). However, the present invention is not limited to those.

EXAMPLE

The present invention is described in more detail by reference to thefollowing Examples, but it should be understood that the invention isnot construed as being limited thereto.

Example 1

Synthesis and Thermal Decomposition Characteristic of(ethylcyclopentadienyl)bis-(ethylene)iridium:

49 mg of di μ-chlorotetrakis(ethylene)diiridium (I) was added to 10 mlof THF, and a reaction flask was cooled to −78° C., to which 10 ml of aTHF solution of 17 mg of lithium ethylcyclopentadienide was then added.The resulting mixture was stirred at −78° C. for 30 minutes, thetemperature was then gradually elevated to room temperature, and theresulting mixture was further reacted for 1 hour, followed byconcentration to obtain a muddy mixture. The muddy mixture was subjectedto extraction with hexane, and the extract solution was subjected tocolumn chromatography (eluant: hexane) using alumina to obtain 14 mg ofthe desired (ethylcyclopentadienyl)bis(ethylene)iridium.

Pale Yellow Oily Material

¹H-NMR (500 MHz, Benzene-d6, δ ppm):

4.78-4.77 (m, 2H), 4.66-4.65 (m, 2H), 2.60-2.58 (m, 4H), 1.90 (q, J=2.5Hz, 2H), 0.94 (t, J=2.5 Hz, 3H), 0.94-0.91 (m, 4H)

IR (neat, cm⁻¹):

3040, 2970, 2920, 2870, 1480, 1460, 1435, 1310, 1165, 1150, 1035, 1010,990, 810, 790

MS (GC/MS, EI):

Molecular ion peak of (ethylcyclopentadienyl)bis(ethylene)iridium interms of ¹⁹³Ir: m/z 342 (FIG. 1)

The result of measuring decomposition characteristic of this compound isshown in FIG. 2. As is apparent from FIG. 2, the organometallic iridiumcompound of the present invention has a decomposition initiationtemperature in the vicinity of 220° C., and therefore can be decomposedat lower temperature than the compound (conventional compound) obtainedin Comparative Example 1 described hereinafter.

The measurement conditions are as follows.

Measurement method: Power compensation differential scanning calorimetry(DSC)

Measurement conditions:

-   -   Reference: Alumina    -   Inert gas: Nitrogen, 50 ml/min    -   Temperature rising: 10° C./min

Comparative Example 1

Thermal Decomposition Characteristic of(ethylcyclopentadienyl)(1,5-cyclooctadiene)iridium:

Decomposition characteristic of(ethylcyclopentadienyl)(1,5-cyclooctadiene)-iridium (conventionalcompound) was measured in the same manner as in Example 1. The resultobtained is shown in FIG. 3. As is apparent from FIG. 3, thisconventional product has a decomposition initiation temperature in thevicinity of 370° C.

Example 2

Synthesis of (methylcyclopentadienyl)bis(ethylene)iridium:

0.97 g of di μ-chlorotetrakis(ethylene)diiridium (I) was added to 50 mlof THF, and a reaction flask was cooled to −78° C., to which 50 ml of aTHF solution of 178 mg of lithium methylcyclopentadienide was thenadded. The resulting mixture was stirred at −78° C. for 1 hour and 40minutes, the temperature was then gradually elevated to roomtemperature, and the resulting mixture was further reacted for 1 hour,followed by concentration to obtain a muddy mixture. The muddy mixturewas subjected to extraction with hexane, and the extract solution wassubjected to column chromatography (eluant: hexane) using alumina toobtain 409 mg of the desired(methylcyclopentadienyl)bis(ethylene)iridium.

Milky White Solid

¹H-NMR (500 MHz, Benzene-d6, δ ppm):

4.84 (t, J=2.0 Hz, 2H), 4.59 (t, J=2.0 Hz, 2H), 2.55-2.44 (m, 4H), 1.51(s, 3H), 0.95-0.93 (m, 4H)

MS (GC/MS, EI):

Molecular ion peak of (methylcyclopentadienyl)bis(ethylene)iridium interms of ¹⁹³Ir: m/z 328 (FIG. 4)

Example 3

Production of Iridium Film using(ethylcyclopentadienyl)bis(ethylene)iridium:

An equipment shown in FIG. 5 was used, and a Si substrate in which aSiO₂ film of 100 nm had been formed on the surface thereof was used as asubstrate 4. About 10 g of (ethylcyclopentadienyl)bis(ethylene)iridiumwas charged in a precursor container 1, and the container was heatedwith an oil bath 2 to make 50° C. constant temperature state. Using avacuum pump 11 and pressure control valves, a reaction chamber 3 wasadjusted at 10 Torr, and the precursor container 1 was adjusted at 100Torr. Nitrogen was used as a carrier gas 7, and its flow rate was set upat 100 sccm by a mass flow controller 10. Oxygen was used as anoxidation gas 5, and nitrogen was used as a counter gas 6. The flow rateof the oxidation gas was set up at 10 sccm by a mass flow controller 8,and the flow rate of the counter gas was set up at 90 sccm by a massflow controller 9. The substrate 4 was set up at 400° C., and subjectedto film formation for 60 minutes while maintaining the heated state. Thefilm formed was metallic iridium film, and its film thickness was 300nm.

Although the present invention is described in detail and by referenceto the specific embodiments, it is apparent to one skilled in the artthat various modifications or changes can be made without departing thespirit and scope of the present invention.

This application is based on Japanese Patent Application No. 2003-295329filed Aug. 19, 2003, No. 2003-383169 filed Nov. 12, 2003, and No.2004-5503 filed Jan. 13, 2004, the disclosures of which are incorporatedherein by reference in their entireties.

INDUSTRIAL APPLICABILITY

The organometallic iridium compounds of the present invention are liquidunder gas bubbling conditions in the case of using CVD process as aprocess for preparing iridium-containing films, so that those canquantitatively be supplied. Furthermore, the organometallic iridiumcompounds can be thermally decomposed at a temperature lower than thatin the conventional materials. As a result, an iridium-containing filmhaving excellent step coverage can be formed on a substrate. The presentinvention makes it possible to prepare iridium-containing films havingexcellent mass-productivity.

1. An organometallic iridium compound represented by the followinggeneral formula (1):

wherein R₁ represents hydrogen atom or a lower alkyl group; and R₂represents a lower alkyl group.
 2. The organometallic iridium compoundas claimed in claim 1, wherein R₁ is hydrogen atom.
 3. A process forproducing the organometallic iridium compound as claimed in claim 1 or2, which comprises reacting a compound represented by the followinggeneral formula (4):

wherein R₂ represents a lower alkyl group, and M represents an alkalimetal with a compound represented by the following general formula (2)or a compound represented by following general formula (3):

wherein R₁ represents hydrogen atom or a lower alkyl group, and Xrepresents a halogen atom,

wherein R₁ and X are the same as defined above.
 4. The process asclaimed in claim 3, wherein R₁ is hydrogen atom.
 5. A process forpreparing iridium-based films, which comprises using, as a precursor,the organometallic iridium compound as claimed in claim 1 or
 2. 6. Theprocess as claimed in claim 5, wherein R₁ is hydrogen atom.